I. Field of the Invention
The present invention relates generally to motorized concrete finishing machines. More particularly, the present invention relates to a guard clearance system for motorized trowels that will maintain the trowel in a spaced apart relationship with a wall (or other obstacle) while allowing finishing of a slab surface immediately adjacent the wall. Known self-propelled trowels are classified in United States Class 404, Subclass 112.
II. Description of the Prior Art
As will be recognized by those skilled in the art, it is well known that wet concrete must be appropriately finished. Motorized trowels are well known as machines for finishing wet concrete. Generally, motorized trowels come in two configurations, riding and manual walk-behind trowels. Each type of trowel employs finishing blades that rest directly on the concrete surface to be finished and that support the machine's entire weight. A wide variety of manually pushed troweling machines have previously been proposed. However, self-propelled riding trowels are preferred because they finish the concrete quicker and more efficiently. Motorized trowels generally employ pivoting blades. The trowel is passed over the concrete surface several times as the concrete sets. The pitch of the blades is adjusted for each pass.
Riding trowels generally include some form of frame from which two or more rotors downwardly project. Each rotor has three or four horizontally oriented, symmetrically disposed blades. The rotors are propelled by a self contained motor mounted on the frame that may be linked to rotor gear boxes. A yoke controlled bearing assembly is often employed to vary blade pitch. The weight of the trowel and the operator is transmitted frictionally to the concrete by the revolving blades. The operator sits on top of the frame and controls the movement of the trowel through a steering system. Steering is accomplished by tilting the blade assemblies to generate differential vector forces. The forces propel the frame across the concrete.
The present assignee, Allen Engineering, owns several prior motorized trowels and related improvements that may be considered relevant to the present invention. U.S. Pat. No. 4,577,993 issued on Mar. 25, 1986, discloses a power trowel with a cam actuated blade pitch adjustment mechanism. Another patent issued to Allen is U.S. Pat. No. 5,108,220 which is directed to a fast steering system for riding trowels. U.S. Des. Pat. No. D. 323,510 also discloses a riding trowel. The latter two patents each disclose, in detail, a guard system typical of those employed on riding trowels.
Riding trowels typical of those present in the art are disclosed in two patents issued to Holz, U.S. Pat. Nos. 4,046,484 and 3,936,212. '212 is a three rotor riding trowel while '484 is a more popular two rotor trowel. Each of the rotors in the Holz patents has three radially spaced apart blades. The blades are guarded by stationary outer rings and inwardly projecting frame members. In the '212 reference, inner rings are also employed to guard the blades.
Guard cages such as those disclosed in the above referenced patents are necessary to protect workers from the rotating blades and to protect the blades from striking rigid structures which could damage the blades. For example, it is more desirable for the cage to strike an obstruction, such as a column, than the blades. This prevents damage to the blades and the motor of the trowel. However, the use of such a guard cage makes finishing surfaces near obstructions and walls difficult.
Maass, U.S. Pat. No. 4,027,991, assigned to M-B-W, Inc., discloses a manually pushed power trowel with a rigid, relieved guard ring section. This section when retracted can slide along a wall during finishing operations to prevent contact between the blades and the wall. However, such a rigid section may "hang up" on a minor wall protrusions or imperfection. The rigid, retracted section could also easily damage the walls by scarring or discoloring it.
In the past, riding trowels failed to provide sufficient control to finish tight areas, such as a slab near the base of a wall. Therefore, it was unnecessary to provide a method for using riding trowels immediately adjacent walls or other structures. The advent of more easily controllable riding trowels, such as the trowel disclosed in aforementioned U.S. Pat. No. 5,108,220, renders the finishing of tight areas using a riding trowel more practical.
Hence, it is desirous to provide an improved guard clearance system for motorized riding trowels. Such a system would provide a portion of trowel guard that would move to a retracted position, exposing a segment of the finishing blade sweep. This exposed segment would then be maneuvered into close proximity with an obstacle, such as a column, curb or wall, to finish the concrete adjacent the obstacle. The displaceable coupling between the retractable portion of the guard and the trowel is either manually or electromechanically manipulated. The guard clearance system should also employ a buffer system to allow the trowel to contact a wall and move along the wall. Such a buffer system would facilitate finishing adjacent to the wall while still protecting the blades by preventing contact with the wall. An ideal buffer system would also work with a manually pushed power trowel.